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Borrowings - Additional Information (Detail) (USD $)
6 Months Ended 3 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Jun. 30, 2013
Junior Subordinated Debenture Due January 31, 2068 [Member]
Mar. 31, 2013
Unsecured Senior and Subordinated Notes [Member]
M&T Bank [Member]
Mar. 31, 2013
Floating Rate Senior Notes Due March 2016 [Member]
M&T Bank [Member]
Mar. 31, 2013
Fixed Rate Senior Notes Due March 2018 [Member]
M&T Bank [Member]
Schedule Of Borrowings [Line Items]            
Junior subordinated debentures face value $ 1,200,000,000          
Percentage of outstanding securities in Tier 1 capital in 2015 25.00%          
Percentage outstanding securities included in tier one capital beginning in 2016 0.00%          
Junior subordinated debentures     350,000,000      
Junior Subordinated Debentures Maturity Date Jan. 31, 2068          
Debt Maturity, Start Year Jan. 01, 2027          
Debt Maturity, End Year Dec. 31, 2068          
Maximum unsecured senior and subordinate notes available for offering       5,000,000,000    
Maturity of unsecured senior and subordinate notes from the date of issue       270 days or more    
Senior notes         300,000,000 500,000,000
Term of senior notes, year         3 years 5 years
Interest rate of senior notes           1.45%
Maturity period of senior notes         2016-03 2018-03
Agreements to repurchase securities 1,400,000,000 1,400,000,000        
Collateral posted $ 1,600,000,000 $ 1,600,000,000